With the growth of online purchasing, shipment of articles of trade having complex geometries is increasing. One of the known methods often used by large retail chains is packing equipment using specially designed Styrofoam inserts, but these inserts are unavailable to stores with limited series of fragile items or with items customized for each end user. Other packaging methods include the use of air cushions, cardboard inserts, or Styrofoam chips. All these methods require storage of bulky packing materials in an area dedicated to packaging within a shipment room. These methods also suffer from human error; for example, Styrofoam chips may be omitted on one side of an object or may migrate within a box during transportation due to low-frequency vibration.
Foam-in-bag packaging techniques offer a possible solution to this storage problem. Two liquids, called precursors, are mixed in controlled quantities when foam is needed in low volume. The liquids react chemically to form a polymer-based foam and gas byproducts. One of the most commonly used pairs of precursors is the isocyanate-based precursor and the polyol-based precursor. These two compounds react to form a urethane polymer called polyurethane. Byproducts of this reaction include steam (water and heat), fluorocarbons, and carbon dioxide. The formation of byproducts is both necessary and unavoidable and must be controlled to obtain the desired foam density and strength since the polyurethane foam is a three-dimensional matrix of gas bubbles held in place by polyurethane.
In the best of conditions, the precursors are mixed instantly and expand fully within an infinite volume. After about ten seconds of mixing, foaming begins, the mixture expands for about fifteen to twenty seconds, and it hardens after about one minute. In less than optimal conditions, the precursors are partly mixed, are partly constrained by storage packaging, and are warped into shape around objects.
In a first generation of foam-in packaging devices, the foam precursors are injected directly into containers, such as corrugated boxes or molds. Because these containers are not airtight, leaks are frequently observed and gaseous byproducts can evacuate the volume freely. In later generations, precursors were injected in plastic bags that allow for shape-change during expansion. The bags could be placed in boxes, and as the foam expanded, the bag would fill in. If timing is managed properly, the item to be packaged, if not too heavy, could rest on the viscous, unsolidified foam. Such bags must include vents for releasing excess gaseous byproducts into the surrounding space. These technologies require the management and manipulation by an operator of the two liquid precursors, along with the plastic bags. If operators place too much liquid in the bag or do not mix the precursors in the correct proportions, the resulting foam can be less than optimal.
In new foam-in-bag inventions, the precursors are placed within sealed pouches and can be mixed when adjacent pouches are ruptured with an external force, such as hand pressure or foot pressure. To create a homogeneous foam within a volume to be packaged, the foam must be allowed to expand continuously during the expansion period and not be subject to pressure waves in the container, where expanding foam must defeat confinement barriers. For example, a first prior art reference discloses how inner pouches can be placed within an outer pouch, which is in turn placed inside the shipping container to be filled with foam. Under this early configuration, the liquid from the bags did not mix absent manipulation by the user. The outer pouch, once filled with partly expanded foam, increases in size and pressure until it bursts, often following an uncontrolled path. A second prior art reference discloses the use of two precursor packets joined and sealed within the pouches by frangible seals. Since no preferred path of release is contemplated, external frangible seals break before the frangible seal located between both precursor zones breaks. Finally, a last prior art reference teaches how an external bag can be formed with fixed internal pockets having frangible seals to draw the precursor liquids into a mixing zone. This technology requires the engineering, use, and testing of multicompartment bags with complex technology requiring manipulation of the precursor fluids during manufacture.
What is needed is a foam-in-bag packaging system that enhances the mixing of the precursor liquids, controls the flow of the foam during expansion and hardening, prevents the formation of pressure walls that overly compress the foam, and can be implemented in containers of simple geometry.